end-Hall Ion Source Research Articles

Effects of Ion Beam Treatment on DC Flashover Characteristics of Epoxy

The effect of ion beam treatment on surface flashover characteristics of epoxy is evaluated and explored. Epoxy samples are prepared and ion beam treatment is carried out for 10-, 15-, 20-, 25-, and 30-min durations using an end-Hall ion source. Flashover test of both pristine and treated samples is conducted at negative dc voltage in air. The results indicate the effectiveness of ion beam treatment to enhance the flashover properties of epoxy. The flashover voltage of the epoxy resin increased to 21.35% after ion beam treatment for a duration of 20 min. Optical microscopic images, scanning electron microscopy (SEM) images, and results from Fourier transform infrared spectroscopy reveal the change in physicochemical characteristics of epoxy resin after treatment. The obtained surface potential from the surface potential decay (SPD) test shows a faster decay rate of surface charges for treated samples than the pristine epoxy. Moreover, from the trap distribution characteristics, it is found that ion beam treatment reduces the surface trap depth, which increases the surface conductivity of the epoxy insulator and helps to promote the charge migration and transport along the insulator surface.

Characteristics of the Raman spectra of diamond-like carbon films. Influence of methods of synthesis

Hydrogenated carbon films were synthesized on single-crystal silicon substrates by an END–Hall ion source or by a linear anode layer source. The gaseous precursors were CH4 and C3H8. The flow rates ranged from 4.5 to 10 sccm. In films synthesized from ion beams, amorphous phase was most pronounced. Carbon films were deposited onto silicon using pulse cathodic arc technique. In these films ordered-structure elements were identified. Raman spectra of a-C and a-C:H films were investigated with the aim of elucidating the interrelation between the hardness of the films (which reached 18, 20, and 45 GPa) and their microstructure.

Fabrication and characterization of adherent diamond-like carbon based thin films on polyethylene terephthalate by end hall ion beam deposition

This work aims to develop novel techniques, including low energy end-hall ion (EDH) source, nitrogen and silicon doping, to enhance the adhesion strength of Diamond-like carbon (DLC) on Polyethylene Terephthalate (PET) to address their major application issues. For this purpose, Nitrogen doped DLC (N-DLC) and Silicon doped DLC (Si-DLC) thin films with different compositions were prepared on PET substrates using EDHI beam deposition. The composition and bonding states of the films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS). The results show that sp3 carbon bonding concentration in Si-DLC is higher than in N-DLC and the doped Si forms sp3 SiC bonds and N forms sp3 CN and sp2 CN bonds in films. Nano-indentation tests were used to measure the hardness and Young's modulus while pin-on-disk sliding tests and scratching tests were used to evaluate the tribological and adhesion behavior of the samples, respectively. The results illustrate hardness reduction and adhesion enhancement in N-DLC and hardness enhancement of Si-DLC. In addition, the coefficient of friction (COF) of N-DLC is lower than pure DLC and Si-DLC, while it has been observed that formation of silicon oxide can reduce COF of Si-DLC. The coating roughness measured by an optical profiler decreases by increasing nitrogen concentration in N-DLC. This is probably because N doping reduces residual stress and thus makes film dense and smooth. By optimizing deposition condition, highly adherent DLC based thin films on PET have been achieved.

Fabrication of superconducting Mo/Cu bilayers using ion-beam-assisted e-beam evaporation.

Superconducting/normal metal bilayers with tunable transition temperature are a critical ingredient to the fabrication of high performance transition edge-sensors (TES). Popular material choices include Mo/Au and Mo/Cu, which exhibit good environmental stability and provide low resistivity films to achieve adequate thermal conductivity. The deposition of high quality Mo films requires sufficient adatom mobility, which can be provided by energetic ions in sputter deposition, or by heating the substrate in an e-beam evaporation process. The bilayer T c depends sensitively on the exact deposition conditions of the Mo layer and the superconducting/normal metal interface. Because the individual contributions (strain, crystalline structure, contamination) are difficult to disentangle and control, reproducibility remains a challenge. Recently, we have demonstrated that low energy ion beam assist during e-beam evaporation offers an alternative route to reliably produce high quality Mo films without the use of substrate heating. The energy and momentum delivered by the ion beam provides an additional control knob to tune film properties such as resistivity and stress. In this report we describe modifications made to the commercial end-Hall ion-source to avoid iron contamination allowing us to produce superconducting Mo films. We show that the ion beam is effective at enhancing the bilayer interface transparency and that bilayers can be further tuned to reduced T c and higher conductivity by vacuum annealing.

Material-related effects during ion beam treatment by an end-Hall ion source

Reproducibility and accuracy of dry etching processes are a challenge for the operators of end-Hall ion sources with hot filament (HF) neutralizer. The variation of the neutralization current IN, e.g. due to filament aging as well as the properties of the substrate material lead to changes in the resulting etch rate of the substrate. Therefore a special controller setup was developed to automatically neutralize the ion beam of an end-Hall ion source with HF by measurement of the substrate current and control of an introduced difference current (ID). In this study, the influence of conductive (amorphous CuTi-film), semi-conductive (B-doped Si(100)) and non-conductive material (128°YX LiNbO3) on ID is demonstrated. Additionally, the etch rate for a wide process regime (VA and IA) for Si(100), the surface roughness for defined under- and overneutralization and the properties of the etched sidewalls were investigated. The effect of the gas distributor ring material on the etch rate is also shown.

Joint functioning of a magnetron sputtering system and an end-hall ion source

The features of joint operation of a magnetron sputtering system (MSS) and an end-Hall ion source (EHIS) are investigated. It is noted that the initiation of the magnetron discharge leads to partial or complete neutralization of the ion beam generated by the EHIS; in other words, in some regimes of the MSS, the ion source operates in the filament-free regime. In such a case, the magnetron discharge is the source of electrons required for sustaining the discharge and for compensating the ion beam from the EHIS. The dependences of the discharge characteristics of the EHIS and MSS are established when a filament neutralizer and MSS discharge are used for compensating the EHIS ion beam. The balance of currents in the ion source-magnetron sputtering system is considered by analyzing the joint functioning of the MSS and EHIS. It is shown that the maximal discharge current from the ion source for which the charge compensation condition is preserved depends on the unbalance and the magnetron discharge current.

Effect of Emitting Current Ion Source on Structural, Optical and Electrical Properties of Nanostructured ITO Thin Films by Ion-Beam Assisted Evaporation

Transparent conductive oxides (TCOs) with indium tin oxide (ITO) thin films were deposited without substrate heating and post-deposition anneal using ion-beam assisted evaporation technique on glass and silicon substrates. The oxygen ion with emitting current produced using End-Hall ion source for bombardment of growing surface to improve ITO films structure. In this study, we investigate the effect of an ion flux to ITO films in terms of structural, optical and electrical properties. The emitting current can be varied from 0.5 to 2.0 A with the oxygen flow rate 7 sccm. The total film thickness and deposition rate are 200 nm and 0.2 nm/s, respectively. The structural properties of thin films were characterized by X-ray diffraction (XRD) to discover the preferred orientation with phase of crystalline and scanning electron microscopy (SEM) to examine the surface morphology in cross-section view. To determine the transmission spectra of the films, UV-visible spectrometer is introduced. Moreover, the films were also measured to investigate resistivity, carrier concentration, mobility and sheet resistance by Hall-effect measurements and four-point probe. It has been found that the ITO films with lowest electrical resistivity for the emitting current of 1 A about 5.57x10-4 Ω.cm and slightly increases with increase of the emitting current. The mobility and carrier concentration rapidly decreases with increase the emitting current from 1.0 A to 2.0 A.

Numerical study of the characteristics of the ion and fast atom beams in an end-Hall ion source

An end-Hall ion source is a cylindrical magnetized device of few centimeters in length able to generate an ion beam with a current of typically 1 A and ion energies in the range of 100 eV. This ion source does not use acceleration grids, has a relatively large ion beam divergence, and is well suited for ion assisted deposition processes. In this paper, a self-consistent two-dimensional quasi-neutral model of an end-Hall ion source is used to understand the parameters controlling the characteristics of the extracted. The model results underline the role of charge exchange collisions on beam properties. The calculated energy distribution functions reveal the existence of groups of slow ions and fast neutrals. Ion mean energy corresponds to roughly 60% of the discharge voltage, while the root mean square deviation from the mean energy corresponds to about 33% of the discharge voltage, as in experiments. The influence of the position of the electron emitting source on the ion angular distribution is also shown.

Plasma transport across magnetic field lines in low-temperature plasma sources

Plasma transport across magnetic field lines plays a key role not only in hot fusion plasmas but also in low-temperature plasma sources operating at low pressure, which often rely on external magnetic fields for their operation. Transport in these sources involves different physics than that in fusion plasmas: the ions are not (completely) magnetized, the plasma is sensitive to wall effects because the magnetic field lines intercept the chamber walls, and the neutral gas density is often much larger than the plasma density. This paper gives an overview of the main principles of magnetized low-temperature plasma transport as they are currently understood, including recent insights on the role of magnetic drift. Three important forms of magnetized low-temperature plasma transport are discussed: magnetized plasma diffusion, transport in E × B fields and magnetic drift. These phenomena are illustrated with recent numerical modeling results on a dipolar microwave source, an End-Hall ion source, and simplified version of the ITER negative ion source. For the latter source it is shown that obstructed magnetic drift can lead to plasma asymmetry and increased cross-field transport.

Physics and modeling of an end-Hall (gridless) ion source

In an end-Hall source, an ion beam is extracted from a magnetized plasma and accelerated by the plasma electric field without grids. The principle of end-Hall sources is similar to that of Hall effect thrusters (or closed-drift thrusters), but their design is optimized for processing applications (ion beam assisted deposition or substrate cleaning) rather than propulsion. The beam divergence is larger in end-Hall ion sources, and these sources can operate at low ion energies. Although end-Hall sources are commonly used in the surface processing industry, no detailed modeling of these sources is available, and their operation is quite empirical. In this paper, a self-consistent, two-dimensional, quasineutral model of an end-Hall ion source is developed and used in order to improve the understanding of the basic physics of these plasma sources and to quantify the parameters controlling the properties of the extracted ion beam.

Characterization of hydrogenated amorphous carbon thin films by end-Hall ion beam deposition

Pure hydrogenated amorphous carbon (α-C:H) and nitrogen doped hydrogenated amorphous carbon (α-C:H:N) thin films were prepared using end-Hall (EH) ion beam deposition with a beam energy ranging from 24eV to 48eV. The composition, microstructure and mechanical properties of the films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning probe microscopy (SPM), and nano-scratch tests. The films are uniform and smooth with root mean square roughness values of 0.5–0.8nm for α-C:H and 0.35nm for α-C:H:N films. When the ion energy was increased from 24eV to 48eV, the fraction of sp3 bonding in the α-C:H films increased from 36% to 55%, the hardness increased from 8GPa to 12.5GPa, and the Young's modulus increased from 100GPa to 130GPa. In the α-C:H:N films, N/C atomic ratio, the hardness and Young's modulus of the α-C:H:N films are, 0.087, 15 and 145GPa, respectively. The results indicate that both higher ion energy and a small amount of N doping improve the mechanical properties of the films. The results have demonstrated that smooth and uniform α-C:H and α-C:H:N films with large area and reasonably high hardness and Young's modulus can be synthesized by EH ion source.

Anti-reflective effect of transparent polymer by plasma treatment with end-hall ion source and optical coating

The surface of poly(methyl methacrylate) (PMMA) was treated by plasma with an end-Hall ion source in vacuum in order to enhance its anti-reflectivity. The cone-shaped bumps induced by the plasma etching have shown an antireflective effect. Moreover, PMMA has poor thermal durability due to its low melting point; therefore, the etched PMMA was further coated by a 5 nm thick SiO2 film after 900 and 1300 s plasma etching. Samples after SiO2 coating were thermally annealed at temperature of 70°C for 1 h. Experiments show that transmittance was increased after 5 nm thick SiO2 coating. The of transmittance of PMMA after both sides treated by 900 s plasma etching and 5 nm SiO2 coating was not changed after thermal annealing. However, without SiO2 coating the transmission was reduced 1% after annealing. Atomic force microscope (AFM) demonstrated that the nano-structures of cone-shaped bumps were formed on the PMMA after plasma etching and a smoother nano-structured pattern preserved the transmittance of the PMMA after both sides treated by 900 s plasma etching and 5 nm SiO2 coating. Three dimensional photonic crystal formed by uniformly distributed cone-shaped bumps was assumed to result in the reduction of the anti-reflectivity of treated PMMA.

Neutralization of an ion beam from the end-Hall ion source by a plasma electron source based on a discharge in crossed E × H fields

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm2 at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O2 or N2. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).

AlF 3 film deposited by IAD with end-Hall ion source using SF 6 as working gas

A novel and effective process to fabricate high quality fluoride thin films was presented. Aluminum fluoride films deposited by a conventional thermal evaporation with an ion-assisted deposition (IAD) using SF 6 as a working gas at around room temperature were investigated. In this study, the optimal voltage and current, 50 V and 0.25 A, were found according to the optical properties of the films: high refractive index (1.489 at 193 nm), low optical absorption and extinction coefficient (<10 −4 at 193 nm) in the UV range. The physical properties of the film are high packing density and amorphous without columnar structure. It was proved that using SF 6 working gas in IAD process is a good choice and significantly improves the quality of AlF 3 films.

Influence of Deposition Method on Refractive Index of SiO2and TiO2Thin Films for Anti-reflective Multilayers

Anti-Reflective (AR) thin film coatings of SiO₂ (n=1.48) and TiO₂ (n=2.17) were deposited by ion-beam assisted deposition (IBAD) with End-Hall ion source and conventional electron beam (e-beam) evaporation to investigate the effect of deposition method on the refractive indicies (n) of the films. Green-light generation using a GaAs laser diode was achieved via excitation of the second harmonic. The latter resulted from the transmission of the fundamental guided-mode wave of 1064 nm through periodically poled LiNbO₃. Large differences in the refractive indicies of each of the layers in the multilayer coating may improve AR performance. IBAD of SiO₂ reduced its refractive index from 1.45 to 1.34 at 1064 nm. Conversely, e-beam evaporation of TiO₂ increased its refractive index from 1.80 to 2.11. In addition, no fluctuations in absorption at the wavelength of 1064 nm were found. The results suggest that films prepared by different deposition methods can increase the effectiveness of multilayer AR coatings.

Comment on “Effects of magnetic field gradient on ion beam current in cylindrical Hall ion source” [J. Appl. Phys. 102, 123305 (2007)

It is argued that the key difference in the cylindrical Hall thruster (CHT) as compared to the end-Hall ion source cannot be exclusively attributed to the magnetic field topology [Tang et al., J. Appl. Phys. 102, 123305 (2007)]. With a similar mirror-type topology, the CHT configuration provides the electric field with nearly equipotential magnetic field surfaces and a better suppression of the electron cross-field transport, as compared to both the end-Hall ion source and the cylindrical Hall ion source of [Tang et al., J. Appl. Phys. 102, 123305 (2007)].

The Atomic Oxygen Erosion Depth and Cone Height of Various Materials at Hyperthermal Energy

Atomic oxygen readily reacts with most spacecraft polymer materials exposed to the low Earth orbital (LEO) environment. If the atomic oxygen arrival comes from a fixed angle of impact, the resulting erosion will foster the development of a change in surface morphology as material thickness decreases. Hydrocarbon and halopolymer materials, as well as graphite, are easily oxidized and textured by directed atomic oxygen in LEO at energies of ∼4.5 eV. What has been curious is that the ratio of cone height to erosion depth is quite different for different materials. The formation of cones under fixed direction atomic oxygen attack may contribute to a reduction in material tensile strength in excess of that which would occur if the cone height to erosion depth ratio was very low because of greater opportunities for crack initiation. In an effort to understand how material composition affects the ratio of cone height to erosion depth, an experimental investigation was conducted on 18 different materials exposed to a hyperthermal energy directed atomic oxygen source (∼70 eV). The materials were first salt-sprayed to provide microscopic local areas that would be protected from atomic oxygen. This allowed erosion depth measurements to be made by scanning microscopy inspection. The polymers were then exposed to atomic oxygen produced by an end Hall ion source that was operated on pure oxygen. Samples were exposed to an atomic oxygen effective fluence of 1.0 1 1020 atoms cm -2 based on Kapton H polyimide erosion. The average erosion depth and average cone height were determined using field emission scanning electron microscopy (FESEM). The experimental ratio of average cone height to erosion depth is compared to polymer composition and other properties.

Inverted end-Hall-type low-energy high-current gaseous ion source

A novel approach to low-energy, high-current, gaseous ion beam generation was explored and an ion source based on this technique has been developed. The source utilizes a dc high-current (up to 20 A) gaseous discharge with electron injection into the region of ion generation. Compared to the conventional end-Hall ion source, the locations of the discharge anode and cathode are inverted: the cathode is placed inside the source and the anode outside, and correspondingly, the discharge current is in the opposite direction. The discharge operates in a diverging axial magnetic field, similar to the end-Hall source. Electron generation and injection is accomplished by using an additional arc discharge with a "cold" (filamentless) hollow cathode. Low plasma contamination is achieved by using a low discharge voltage (avoidance of sputtering), as well as by a special geometric configuration of the emitter discharge electrodes, thereby filtering (removing) the erosion products stemming from the emitter cathode. The device produces a dc ion flow with energy below 20 eV and current up to 2.5 A onto a collector of 500 cm(2) at 25 cm from the source edge, at a pressure > or =0.02 Pa and gas flow rate > or =14 SCCM. The ion energy spread is 2 to 3 eV (rms). The source is characterized by high reliability, low maintenance, and long lifetime. The beam contains less than 0.1% of metallic ions. The specific electric energy consumption is 400 eV per ion registered at the collector. The source operates with noble gases, nitrogen, oxygen, and hydrocarbons. Utilizing biasing, it can be used for plasma sputtering, etching, and other ion technologies.

Characteristics of end Hall ion source with magnetron hollow cathode discharge

An end Hall ion source with magnetron hollow cathode discharge is described. The source is suitable for high current, low energy ion beam applications such as Hall current plasma accelerators. The end Hall ion source is based on an anode layer thruster with closed drift electrons that move in a closed path in the E×B field. Only a simple magnetron power supply is used in the ion source. The special configuration enables uninterrupted and expanded operation with oxygen as well as other reactive gases because of the absence of an electron source in the ion source. In our evaluation, the ion beam current was measured by a circular electrostatic probe and the energy distribution of the ion beam was measured by a retarding potential analyzer (RPA). An ion beam current density of up to 10mA/cm2 was obtained at a mean ion energy of 100–250eV using Ar or O2. The ion source can be operated in a stable fashion at a discharge voltage between 200 and 500V and without additional electron triggering. The discharge power of the ion source can be easily changed by adjusting the gas flow rate and anode voltage. No water cooling is needed for power from 500W to 2kW. The simple and rugged ion source is suitable for industrial applications such as deposition of thin films with enhanced adhesion. The operational characteristics of the ion source are experimentally determined and discussed.

Diamond-like carbon films with End-Hall ion source enhanced chemical vapour deposition

A custom-designed End-Hall ion source was used to deposit diamond-like carbon (DLC) films in a plasma enhanced chemical vapour deposition (PECVD) mode. The deposition system was characterised and optimised for infrared transmission enhancement applications and large area deposition onto silicon or germanium substrates. Ion bombardment energy (in eV) on substrate was found to scale about 60% of the discharge voltage. Uniformity was about 2.5% and 5% for substrate diameters of 20 cm and 40 cm respectively. For the infrared enhancement applications the optimised ion bombardment energy was about 54 eV with a high deposition rate approximate 30 nm/min. Coating the DLC onto a single side of double-sided polished silicon wafers resulted in a transmission of 69.5% in the wavelength of about 4 μm, very close to the ideal value. Mechanical and reliability properties of the DLC films on silicon wafers were analysed at different environmental conditions. It was found that the DLC films produced in the ion source PECVD deposition system were satisfied with the requirements for the infrared transmission enhancement applications.